APPARATUS, SYSTEM, AND METHOD FOR REDUCING NOx EMISSIONS ON AN SCR CATALYST

• US 20090272105A1
• Filed: 04/30/2008
• Published: 11/05/2009
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Ofoli, Abdul R., Chi, John N., Wills, Joan M., Hill, Joe V., Farrell, Lisa A., Garimella, Phanindra, Wang, Weiwen
• Granted Patent: US 8,161,730 B2
• Time in Patent Office: Days
• US Class Current: 60/295
• CPC Class Codes: B01D 2251/2062 Ammonia
• CPC Class Codes: B01D 53/9409 Nitrogen oxides
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 2560/026 for measuring or detecting NOx
• CPC Class Codes: F01N 2560/06 the means being a temperature sensor
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2900/1616 NH3-slip from catalyst
• CPC Class Codes: F01N 2900/1622 Catalyst reducing agent absorption capacity or consumption amount
• CPC Class Codes: F01N 3/035 with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/0814 combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0821 combined with particulate filters catalysed diesel particulate filters F01N3/035
• CPC Class Codes: F01N 3/0828 characterised by the absorbed or adsorbed substances
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: F01N 9/00 Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• CPC Class Codes: F02B 37/164 the bypassed air being used in an auxiliary apparatus, e.g. in an air turbine
• CPC Class Codes: F02B 37/18 by bypassing exhaust from the inlet to the outlet of turbine or to the atmosphere
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

Various embodiments of an apparatus, system, and method are disclosed for reducing NO_x emissions on an SCR catalyst. For example, according to one representative embodiment, an apparatus for reducing NO_x emissions in an engine exhaust includes a NO_x reduction target module that is configured to determine a NO_x reduction requirement that includes an amount of NO_x in the exhaust gas stream to be reduced on a selective catalytic reduction (SCR) catalyst. The apparatus also includes an ammonia target module that is configured to determine an ammonia addition requirement that includes an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement. The apparatus also includes a reductant target module that is configured to determine a reductant injection requirement that includes an amount of reductant added to the exhaust gas stream to achieve the ammonia addition requirement. The apparatus further includes a reductant limiting module that is configured to determine whether at least one reductant limiting condition is met and to limit the amount of reductant added in response to the at least one reductant limiting condition if the at least one reductant limiting condition has been met.

Claims

1. An apparatus for reducing no, emissions in an engine exhaust gas stream of an engine system, comprising:

a NO_x reduction target module configured to determine a NO_x reduction requirement, the NO_x reduction requirement comprising an amount of NO_x in the exhaust gas stream to be reduced on a selective catalytic reduction (SCR) catalyst;

an ammonia target module configured to determine an ammonia addition requirement, the ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement;

a reductant target module configured to determine a reductant injection requirement, the reductant injection requirement comprising an amount of reductant added to the exhaust gas stream to achieve the ammonia addition requirement; and

a reductant limiting module configured to determine a reductant limiting requirement representing whether at least one reductant limiting condition has been met;

wherein the reductant target module is communicable in data receiving communication with the reductant limiting module to receive the reductant limiting requirement, the reductant target module being configured to limit the amount of reductant added in response to the reductant limiting requirement.

2. The apparatus of claim 1, wherein the ammonia target module comprises a feedforward ammonia target module and the ammonia addition requirement comprises a first ammonia addition requirement, the apparatus further comprising a feedback ammonia target module configured to determine a second ammonia addition requirement, wherein the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve one of the first and second ammonia addition requirements.

3. The apparatus of claim 2, wherein the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve the first ammonia addition requirement when ammonia is exiting the engine system, and wherein the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve the second ammonia addition requirement when ammonia is not exiting the engine system.

4. The apparatus of claim 1, wherein the ammonia target module comprises a feedforward ammonia target module and the ammonia addition requirement comprises a first ammonia addition requirement, the apparatus further comprising a feedback ammonia target module configured to determine a second ammonia addition requirement, wherein the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve a combination of the first and second ammonia addition cc requirements.

5. The apparatus of claim 1, wherein:

the ammonia target module comprises a feedback ammonia target module; and

the ammonia addition requirement is based at least partially on a comparison between a desired amount of NO_x exiting the engine system and a measured amount of NO_x exiting the engine system.

6. The apparatus of claim 5, further comprising a corrected NO_x module configured to determine a corrected tailpipe NO_x sensor signal based at least partially on input from a tailpipe NO_x sensor and the condition of the tailpipe NO_x sensor, wherein the measured amount of NO_x exiting the engine system is interpreted from the corrected tailpipe NO_x sensor signal.

7. The apparatus of claim 1, wherein the NO_x reduction requirement comprises a fraction of the NO_x in the exhaust gas stream to be reduced to achieve a predetermined emissions limit.

8. The apparatus of claim 1, wherein the ammonia target module is further configured to determine the ammonia addition requirement according to a composition of a total amount of NO_x in the exhaust gas stream, the composition of the total amount of NO_x comprising a ratio

$\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}.$

9. The apparatus of claim 8, wherein:

the reductant comprises urea, and wherein the reductant target module determines the reductant injection requirement as

$\frac{\mathrm{mL}}{\mathrm{hr}}<br><br>\mathrm{Urea};<br><br>$ $\frac{\mathrm{mL}}{\mathrm{hr}}<br><br>\mathrm{Urea}\approx <br><br>1.85*f<br><br>\left(\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}\right)*\stackrel{.}{m}<br><br>{\mathrm{NO}}_x;<br><br>\mathrm{and}$

{dot over (m)}NO_x comprises the total amount of NO_x in the exhaust gas stream expressed in grams/hour;

$\mathrm{wherein}<br><br><br><br><br><br>f\left(\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}\right)=\frac{2<br><br>\left(1+\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}\right)}{3}<br><br><br><br>\mathrm{when}<br><br><br><br>\mathrm{NO}\le <br><br>{\mathrm{NO}}_2,<br><br>\mathrm{and}$ $f<br><br>\left(\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}\right)=1.0<br><br><br><br>\mathrm{when}<br><br><br><br>\mathrm{NO}\ge <br><br>{\mathrm{NO}}_2.$

10. The apparatus of claim 8, wherein:

the ammonia target module is further configured to determine the ammonia addition requirement according to a predicted NO_x reduction reaction rate; and

the predicted NO_x reduction reaction rate comprises a function of a NO_x concentration in the exhaust gas stream, an ammonia concentration in the exhaust gas stream, a bed temperature of the SCR catalyst, and a space velocity of the SCR catalyst.

11. The apparatus of claim 10, wherein the predicted NO_x reduction reaction rate further comprises a function of a degradation factor of the SCR catalyst.

12. The apparatus of claim 10, wherein the predicted NO_x reduction reaction rate comprises a sum of:

a predicted reaction rate for reducing NO and a predicted reaction rate for reducing NO₂.

13. The apparatus of claim 1, wherein the at least one reductant limiting condition comprises at least one limit selected from the group consisting of an exhaust gas temperature limit, an ammonia slip reductant rate limit, and an SCR catalyst bed temperature limit.

14. A method for reducing NO_x emissions in an engine exhaust gas stream of an engine system, the method comprising:

determining a NO_x reduction requirement, the NO_x reduction requirement comprising an amount of NO_x in the exhaust gas stream to be reduced on a selective catalytic reduction (SCR) catalyst;

determining an ammonia addition requirement, the ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement;

determining a reductant injection requirement, the reductant injection requirement comprising an amount of reductant added to the exhaust gas stream to achieve the ammonia addition requirement; and

determining whether at least one reductant limiting condition is met, and if the at least one reductant limiting condition is met, limiting the amount of reductant added in response to the reductant limiting condition.

15. The method of claim 14, wherein determining an ammonia addition requirement comprises comparing a desired amount of NO_x emissions exiting the engine system with a measured amount of NO_x exiting the engine system.

16. The method of claim 14, wherein determining an ammonia addition requirement comprises determining a first ammonia addition requirement based at least partially on a ratio of NO to NO₂ in the exhaust stream prior to entering the SCR catalyst, the amount of NH₃ entering the SCR catalyst, the amount of NO_x entering the SCR catalyst, and a temperature of the SCR catalyst, and determining a second ammonia addition requirement based at least partially on the difference between a desired amount of NO_x emissions exiting the engine system and a measured amount of NO_x exiting the engine system.

17. The method of claim 16, wherein:

the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve the first ammonia addition requirement when ammonia is exiting the engine system; and

wherein the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve the second ammonia addition requirement when ammonia is not exiting the engine system.

18. The method of claim 16, the method further comprising determining a corrected tailpipe NO_x feedback parameter, and wherein the corrected tailpipe NO_x feedback parameter is representative of the measured amount of NO_x exiting the engine system.

19. The method of claim 14, wherein:

the reductant is urea;

determining the ammonia addition requirement further comprises determining the ammonia addition requirement according to a composition of a total amount of NO_x in the exhaust gas stream, the composition of the total amount of NO_x comprising a ratio

$\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2};<br><br>$

when the amount of NO in the exhaust gas stream is more than or equal to the amount of NO₂ in the exhaust gas stream, the urea injection requirement in grams/s is approximately equal to

$\frac{{\stackrel{.}{m}}_{\mathrm{NOx}}}{0.5*\left(\frac{M<br><br><br><br>W_{\mathrm{Urea}}}{M<br><br><br><br>W_{\mathrm{NOx}}}\right)},$

wherein {dot over (m)}_NOx is the mass flow rate of NO_x in the exhaust gas stream in grams/s, MW_urea is the molecular weight of urea, and MW_NOx is the molecular weight of NO_x in the exhaust gas stream; and

when the amount of NO in the exhaust gas stream is less than or equal to the amount of NO₂ in the exhaust gas stream, the urea injection requirement in grams/s is approximately equal to

$\frac{{\stackrel{.}{m}}_{\mathrm{NOx}}}{0.5*\left(\frac{M<br><br><br><br>W_{\mathrm{Urea}}}{M<br><br><br><br>W_{\mathrm{NOx}}}\right)<br><br>\left(\frac{2<br><br>\left(a+1\right)}{3}\right)},$

wherein {dot over (m)}_NOx is the mass flow rate of NO_x in the exhaust gas stream in grams/s, MW_urea is the molecular weight of urea, MW_NOx is the molecular weight of NO_x in the exhaust gas stream, and a is equal to the ratio

$\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}.$

20. The method of claim 14, wherein:

determining the reductant injection requirement further comprises determining the reductant injection requirement as

$\frac{\mathrm{mL}}{\mathrm{hr}}<br><br>\mathrm{Urea};<br><br>$ $\frac{\mathrm{mL}}{\mathrm{hr}}<br><br>\mathrm{Urea}\approx <br><br>1.85*\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}*\stackrel{.}{m}<br><br>{\mathrm{NO}}_x;<br><br>\mathrm{and}$

{dot over (m)}NO_x comprises the total amount of NO_x in the exhaust gas stream expressed in grams/hour;

$\mathrm{wherein}<br><br><br><br>f<br><br>\left(\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}\right)=\frac{2<br><br>\left(1+\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}\right)}{3}<br><br><br><br>\mathrm{when}<br><br><br><br>\mathrm{NO}\le <br><br>{\mathrm{NO}}_2,<br><br>\mathrm{and}$ $f<br><br>\left(\frac{{\mathrm{NO}}_2}{\mathrm{NO}+{\mathrm{NO}}_2}\right)=1.0<br><br><br><br>\mathrm{when}<br><br><br><br>\mathrm{NO}\ge <br><br>{\mathrm{NO}}_2.$

21. The method of claim 14, wherein:

determining the ammonia addition requirement further comprises determining the ammonia addition requirement according to a predicted NO_x reduction reaction rate; and

the predicted NO_x reduction reaction rate comprises a function of a NO_x concentration, an ammonia concentration, a bed temperature of the SCR catalyst, and a space velocity of the SCR catalyst.

22. The method of claim 21, further comprising determining the bed temperature of the SCR catalyst by comparing the temperature of the exhaust at an entrance of the SCR catalyst with the temperature of the exhaust at an exit of the SCR catalyst.

23. A system for reducing NO_x emissions in an engine exhaust, the system comprising:

an internal combustion engine producing an exhaust gas stream;

a selective catalytic reduction (SCR) catalyst that reduces NO_x emissions in the exhaust gas stream in the presence of a reductant;

a reductant injector that injects reductant into the exhaust gas stream upstream of the SCR catalyst;

a controller comprising;

a NO_x reduction target module configured to determine a NO_x reduction requirement, the NO_x reduction requirement comprising an amount of NO_x in the exhaust gas stream to be reduced on the SCR catalyst;

an ammonia target module configured to determine an ammonia addition requirement, the ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement;

a reductant target module configured to determine a reductant injection requirement, the reductant injection requirement comprising an amount of reductant added to the exhaust gas stream to achieve the ammonia addition requirement; and

a reductant limiting module configured to determine whether at least one reductant limiting condition is met, and to limit the amount of reductant added in response to the at least one reductant limiting condition if the at least one reductant limiting condition is met.

24. The system of claim 23, wherein the ammonia target module comprises a feedforward ammonia target module and the ammonia addition requirement comprises a first ammonia addition requirement, the apparatus further comprising a feedback ammonia target module configured to determine a second ammonia addition requirement, wherein the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve the first ammonia addition requirement when ammonia is slipping from the engine system and the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve the second ammonia addition requirement when ammonia is not slipping from the engine system.

25. The system of claim 23, further comprising a NO_x sensor embedded within the SCR catalyst.